In recent years, a swallowable capsule endoscope has been proposed in a field of endoscope. The capsule endoscope has an imaging function and a radio communication function. After being swallowed by a subject from the mouth for an observation (examination), the capsule endoscope travels through inside body cavities, such as internal organs including a stomach and a small intestine following a peristaltic motion of the body cavities, and is eventually discharged naturally from the subject. The capsule endoscope has a function of capturing intra-subject images at 0.5-second intervals, for example, while traveling through the body cavities.
While traveling through the body cavities, the capsule endoscope externally and sequentially transmits image data obtained through the image capturing inside the body to an outside via radio communication, and the image data is accumulated in a memory provided outside. The subject carries a receiver having a radio communication function and a memory function, whereby the subject can move freely after swallowing the capsule endoscope until discharging the capsule endoscope. After the capsule endoscope is discharged, a doctor or a nurse can display images of internal organs based on the image data accumulated in the memory and make diagnosis (for example, see Patent Document 1).
Some propose a capsule endoscope including a string-like member attached to an outer casing portion for traction. FIG. 9 is a schematic diagram of a structure of such a capsule endoscope including a string-like member. Specifically, a capsule endoscope 100 shown in FIG. 9 includes an outer casing member 101 which defines an external shape of the capsule endoscope 100 and which is provided with an imaging window 101a corresponding to a field of view of an imaging unit 104, an attachment member 103 which is formed on the outer casing member 101, and a string-like member 102 having one end connected to the attachment member 103.
The string-like member 102 is employed to pull the capsule endoscope 100 inside the subject from outside. For example, when an operator wants to capture intra-subject images of an esophagus portion using a general capsule endoscope, a fast movement of the capsule endoscope makes it difficult to perform a sufficient imaging operation. When one end of the string-like member 102 is connected to the outer casing member 101 shown in FIG. 9, a doctor, for example, can pull another end of the string-like member 102 to adjust a moving speed and a position of the capsule endoscope 100 inside the subject. When the capsule endoscope has such a structure, it becomes possible to slow down the moving speed of the capsule endoscope for capturing plural intra-subject images even in an area such as an esophagus, and to capture the intra-subject images of an area where the capsule endoscope has already passed through.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-019111